As conventional methods of growing a single crystal, there are known an HB (Horizontal Bridgman) method, a GF (Gradient Freeze) method, a VB (Vertical Bridgman) method, a VGF (Vertical Gradient Freeze) method, a VZM (Vertical Zone Melt) method and the like. In each of these methods, a seed crystal is placed at a part of a boat or a crucible in which a source melt is brought in contact with the seed crystal, and temperature of the melt is gradually lowered on the seed crystal side so as to grow a single crystal. Particularly in the VB method and the VGF method, it is possible to use a cylindrical crucible as shown in Japanese Patent Laying-Open No. 04-367583 (Patent Document 1) and Japanese Patent Laying-Open No. 08-048591 (Patent Document 2).
FIG. 6 is a schematic cross-sectional view showing an exemplary crucible for use in the conventional VB method. A crucible 11 includes a crucible tip portion 3 for accommodating a seed crystal 2, a straight-body portion 5 for growing a crystal product having a diameter larger than that of tip portion 3, and a shoulder portion 4 connecting crucible tip portion 3 and straight-body portion 5. When a compound semiconductor crystal is to be grown, boron nitride is used as a material of the crucible. In an actual procedure of crystal growth, a production apparatus as described below is used with such a crucible.
FIG. 7(A) is a schematic block diagram showing an exemplary crystal production apparatus, while FIG. 7(B) is a graph showing a temperature profile in the apparatus. In the crystal production apparatus of FIG. 7(A), a crucible 11 is set on a crucible installation portion 8 provided at the center of an airtight container 6. Heating portions 7 are provided around crucible 11. Heating portions 7 are controlled to create a temperature profile including a temperature gradient as shown in FIG. 7(B). Under relative movement of the temperature profile, a source is melted to be in contact with a seed crystal and then solidified to grow a single crystal.
In Japanese Patent Laying-Open No. 08-048591, each of the thicknesses and the inside diameters of the tip portion and the straight-body portion of the crystal growth crucible is adjusted within a certain range such that temperature difference in a radial direction of the crystal (between central part and outer peripheral part) during crystal growth is reduced so as to suppress thermal strain and generation of dislocations (crystal defects).
Patent Document 1: Japanese Patent Laying-Open No. 04-367583
Patent Document 2: Japanese Patent Laying-Open No. 08-048591